Fix issue #16803 do not error on getters/setters (#18031)

src/compiler/checker.ts

@@ -497,6 +497,8 @@ namespace ts {
         const builtinGlobals = createSymbolTable();
         builtinGlobals.set(undefinedSymbol.escapedName, undefinedSymbol);
 
+        const isNotOverloadAndNotAccessor = and(isNotOverload, isNotAccessor);
+
         initializeTypeChecker();
 
         return checker;
@@ -22257,7 +22259,7 @@ namespace ts {
                     if (flags & (SymbolFlags.Namespace | SymbolFlags.Interface | SymbolFlags.Enum)) {
                         return;
                     }
-                    const exportedDeclarationsCount = countWhere(declarations, isNotOverload);
+                    const exportedDeclarationsCount = countWhere(declarations, isNotOverloadAndNotAccessor);
                     if (flags & SymbolFlags.TypeAlias && exportedDeclarationsCount <= 2) {
                         // it is legal to merge type alias with other values
                         // so count should be either 1 (just type alias) or 2 (type alias + merged value)
@@ -22273,11 +22275,16 @@ namespace ts {
                 });
                 links.exportsChecked = true;
             }
+        }
 
-            function isNotOverload(declaration: Declaration): boolean {
-                return (declaration.kind !== SyntaxKind.FunctionDeclaration && declaration.kind !== SyntaxKind.MethodDeclaration) ||
-                        !!(declaration as FunctionDeclaration).body;
-            }
+        function isNotAccessor(declaration: Declaration): boolean {
+            // Accessors check for their own matching duplicates, and in contexts where they are valid, there are already duplicate identifier checks
+            return !isAccessor(declaration);
+        }
+
+        function isNotOverload(declaration: Declaration): boolean {
+            return (declaration.kind !== SyntaxKind.FunctionDeclaration && declaration.kind !== SyntaxKind.MethodDeclaration) ||
+                    !!(declaration as FunctionDeclaration).body;
         }
 
         function checkSourceElement(node: Node): void {

src/compiler/core.ts

@@ -2626,4 +2626,8 @@ namespace ts {
     export function isCheckJsEnabledForFile(sourceFile: SourceFile, compilerOptions: CompilerOptions) {
         return sourceFile.checkJsDirective ? sourceFile.checkJsDirective.enabled : compilerOptions.checkJs;
     }
+
+    export function and<T>(f: (arg: T) => boolean, g: (arg: T) => boolean) {
+        return (arg: T) => f(arg) && g(arg);
+    }
 }

tests/baselines/reference/exportEqualsClassNoRedeclarationError.js

@@ -0,0 +1,19 @@
+//// [exportEqualsClassNoRedeclarationError.ts]
+class SomeClass {
+    static get someProp(): number {
+        return 0;
+    }
+
+    static set someProp(value: number) {}
+}
+export = SomeClass;
+
+//// [exportEqualsClassNoRedeclarationError.js]
+"use strict";
+class SomeClass {
+    static get someProp() {
+        return 0;
+    }
+    static set someProp(value) { }
+}
+module.exports = SomeClass;

tests/baselines/reference/exportEqualsClassNoRedeclarationError.symbols

@@ -0,0 +1,17 @@
+=== tests/cases/compiler/exportEqualsClassNoRedeclarationError.ts ===
+class SomeClass {
+>SomeClass : Symbol(SomeClass, Decl(exportEqualsClassNoRedeclarationError.ts, 0, 0))
+
+    static get someProp(): number {
+>someProp : Symbol(SomeClass.someProp, Decl(exportEqualsClassNoRedeclarationError.ts, 0, 17), Decl(exportEqualsClassNoRedeclarationError.ts, 3, 5))
+
+        return 0;
+    }
+
+    static set someProp(value: number) {}
+>someProp : Symbol(SomeClass.someProp, Decl(exportEqualsClassNoRedeclarationError.ts, 0, 17), Decl(exportEqualsClassNoRedeclarationError.ts, 3, 5))
+>value : Symbol(value, Decl(exportEqualsClassNoRedeclarationError.ts, 5, 24))
+}
+export = SomeClass;
+>SomeClass : Symbol(SomeClass, Decl(exportEqualsClassNoRedeclarationError.ts, 0, 0))
+

tests/baselines/reference/exportEqualsClassNoRedeclarationError.types

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/exportEqualsClassNoRedeclarationError.ts ===
+class SomeClass {
+>SomeClass : SomeClass
+
+    static get someProp(): number {
+>someProp : number
+
+        return 0;
+>0 : 0
+    }
+
+    static set someProp(value: number) {}
+>someProp : number
+>value : number
+}
+export = SomeClass;
+>SomeClass : SomeClass
+

tests/baselines/reference/exportEqualsClassRedeclarationError.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/compiler/exportEqualsClassRedeclarationError.ts(2,16): error TS2300: Duplicate identifier 'someProp'.
+tests/cases/compiler/exportEqualsClassRedeclarationError.ts(6,16): error TS2300: Duplicate identifier 'someProp'.
+tests/cases/compiler/exportEqualsClassRedeclarationError.ts(7,16): error TS2300: Duplicate identifier 'someProp'.
+
+
+==== tests/cases/compiler/exportEqualsClassRedeclarationError.ts (3 errors) ====
+    class SomeClass {
+        static get someProp(): number {
+                   ~~~~~~~~
+!!! error TS2300: Duplicate identifier 'someProp'.
+            return 0;
+        }
+    
+        static set someProp(value: number) {}
+                   ~~~~~~~~
+!!! error TS2300: Duplicate identifier 'someProp'.
+        static set someProp(value: number) {}
+                   ~~~~~~~~
+!!! error TS2300: Duplicate identifier 'someProp'.
+    }
+    export = SomeClass;

tests/baselines/reference/exportEqualsClassRedeclarationError.js

@@ -0,0 +1,21 @@
+//// [exportEqualsClassRedeclarationError.ts]
+class SomeClass {
+    static get someProp(): number {
+        return 0;
+    }
+
+    static set someProp(value: number) {}
+    static set someProp(value: number) {}
+}
+export = SomeClass;
+
+//// [exportEqualsClassRedeclarationError.js]
+"use strict";
+class SomeClass {
+    static get someProp() {
+        return 0;
+    }
+    static set someProp(value) { }
+    static set someProp(value) { }
+}
+module.exports = SomeClass;

tests/cases/compiler/exportEqualsClassNoRedeclarationError.ts

@@ -0,0 +1,10 @@
+// @target: es6
+// @module: commonjs
+class SomeClass {
+    static get someProp(): number {
+        return 0;
+    }
+
+    static set someProp(value: number) {}
+}
+export = SomeClass;

tests/cases/compiler/exportEqualsClassRedeclarationError.ts

@@ -0,0 +1,11 @@
+// @target: es6
+// @module: commonjs
+class SomeClass {
+    static get someProp(): number {
+        return 0;
+    }
+
+    static set someProp(value: number) {}
+    static set someProp(value: number) {}
+}
+export = SomeClass;